Hydromorphone is an analgesic with its principal therapeutic effect the relief of pain. The precise mechanism of action of hydromorphone is not known, although it is thought to relate to the existence of hydromorphone receptors in the central nervous system. Generally, the analgesic action of parenterally administered hydromorphone is apparent within fifteen minutes and the onset of action of oral hydromorphone is somewhat slower, with analgesia occurring within thirty minutes. In human plasma, the half-life of hydromorphone is about two and one-half hours. Hydromorphone is indicated for the relief of moderate to severe pain, such as that due to surgery, cancer, trauma, biliary colic, renal colic, myocardial infarction and burns. A pharmaceutically acceptable dosage form for oral administering hydromorphone to provide analgesic therapy beyond its short half-life at a controlled rate over an extended period of time appears to be lacking in the pharmaceutical and medical arts. The pharmacological properties of hydromorphone are known in Pharmaceutical Sciences, Remington, 17th Ed, pp. 1099-1044 (1985); and in the Pharmacological Basis of Therapeutics, Goodman and Rail, 8th Ed, pp 485-518 (1990).